Crystal structure and Hirshfeld surface analysis of N,N′-bis(2-nitrophenyl)glutaramide

The title bis-amide derivative was obtained by the reaction between glutaric acid chloride and 2-nitroaniline. The two benzene rings are twisted by angles of 79.14 (7) and 19.02 (14)° in the two independent molecules. In the crystal, amide–amide interactions link the molecules into chains running along b-axis direction.


Chemical context
Alkanediamide derivatives are known to possess a variety of biological activities. There has been a study on the influence of the length of the connecting chain on the antimalarial activity of bisquinolines (Raynes et al., 1995) and OER (oxygen evolution rate) inhibiting activity in spinach in a series of N,N 0 -bis(3,4-dichlorophenyl)alkanediamides (Kubicova et al., 2000a,b). The crystal structures of a homologous series of bis(pyridinecarboxamido)alkanes have been studied to analyse their supramolecular structures (Sarkar & Biradha, 2006). As a part of a study on substituent effects on the structures of bis-amides, the crystal structure of N,N 0 -bis(2nitrophenyl)glutaramide has been determined and is described in the present work.

Structural commentary
The asymmetric unit of the title compound (I) contains two independent molecules (designated as A and B in Fig. 1), and four molecules in the unit cell. In both the molecules present in the asymmetric unit, all the N-H, C O and C-H bonds of the amide and aliphatic segments are anti to each other. The conformation of the nearest C O group is anti to the orthonitro group in the aniline ring in one half of each molecule, as indicated by the torsion angles of À159.5 (3) and À161.9 (3) for C2-C1-N1-C7 and C19-C18-N5-C24, respectively. In the other half, they are syn to the ortho-substituent as shown by the torsion angles of 48.6 (4) and À50.6 (4) for C13-C12-N2-C11 and C30-C29-N6-C28, respectively. The O1-C7, O2-C11, O7-C24 and O8-C28 bond lengths are 1.213 (3), 1.224 (3), 1.218 (3) and 1.218 (3) Å , respectively, which indicate that the molecules exist in their keto forms in the solid state. In molecule A, the bis-amide group forms dihedral angles of 24.79 (12) and 55.04 (7) with the phenyl rings C1-C6 and C12-C17, respectively. In molecule B, the plane of the amide group forms dihedral angles of 34.24 (13) and 24.27 (12) with the C18-C23 and C29-C34 phenyl rings, respectively, while the two benzene rings form a dihedral angle of 79.14 (7) and 19.02 (14) in molecules A and B, respectively. The planes of molecules A and B are almost coplanar with each other, as is evident from the dihedral angle of only 3.15 (17) between phenyl rings C1-C6 and C18-C23.
The O atoms of the ortho-substituted nitro groups attached to the C1/C6 and C18/C23 phenyl rings form short intramolecular contacts, each of 2.01 (3) Å , with the nearest amide N atom, forming an N-HÁ Á ÁO contact resulting in an S(6) hydrogen bonding motif.

Figure 2
Hydrogen-bonding pattern in (I) with hydrogen bonds shown as dashed lines.

Figure 1
Molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and hydrogen atoms are omitted for clarity.
between two bis-amide groups results in molecular chains running along the b-axis direction. The oxygen atom of the amide C O group in molecule B forms a bifurcated hydrogen bond with the N-H group of the amide unit and the C-H group of the aliphatic chain of an adjacent molecule. The C3-H3 unit of the C1-C6 ring of molecule A forms a short intermolecular contact with the oxygen atom O5 belonging to the nitro group of the C12-C17 phenyl ring of another A molecule at position Àx, 1 À y, Àz. C-H groups of the C12-C17 and C29-C34 phenyl rings form hydrogen bonds with the O atoms of the nitro groups of the C12/C17 and C29/C34 phenyl rings at Àx, Ày + 2, Àz + 1 and Àx + 1, Ày + 1, Àz + 1, respectively. A packing diagram of the title compound is shown in Fig. 3.

Hirshfeld Surface analysis
The intermolecular contacts in the crystal structure were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, generated using CrystalExplorer View of the Hirshfeld surface mapped over d norm for the two independent molecules (A and B). The colour scale is between À0.21 au (red) to 1.2 au (blue).

Figure 5
View of the Hirshfeld surface mapped over the electrostatic potential for the two molecules (A and B).

Figure 3
Molecular packing of (I) with hydrogen bonds shown as dashed lines.

Figure 6
Two-dimensional fingerprint plots for the title compound showing the contributions of different types of interactions In the two-dimensional fingerprint plot (Fig. 6), d i is the closest internal distance from a given point on the Hirshfeld surface to the nearest atom and d e is the closest external contact. The outline of the full fingerprint is shown in grey. The fingerprint plots are used to plot intermolecular contacts with respect to d i and d e . Visualization of the Hirshfeld surfaces and fingerprint plots allow the intermolecular interactions to be quantified. The fingerprint plot of OÁ Á ÁH/HÁ Á ÁO contacts shows two symmetrical narrow pointed wings, which represent the largest contribution to the Hirshfeld surfaces (41.7%), with d e + d i $ 2.4 Å (Fig. 6b). HÁ Á ÁH contacts represent the next largest contribution to the Hirshfeld surfaces (29.2%) and show a distinct pattern with a minimum value of d e = d i $ 1.2 Å (Fig. 6c). OÁ Á ÁC/CÁ Á ÁO and NÁ Á ÁH/ HÁ Á ÁN interactions cover only 5.4% (Fig. 6d) and 3.4% (Fig. 6e) of the surface, respectively. Two triangles featuring the CÁ Á ÁC contacts contribute 3.2% to the Hirshfeld surfaces, with a minimum (d e + d i ) distance of 3.5 Å (Fig. 6f).

Related structures
The structure of bis-amides, namely, 3-methyl; 2-chloropropanediamides (Gowda et al., 2010b,c), N,N 0 -bis(phenyl)suberamide (Gowda et al., 2010a), bis-2-methyl; 2-chloro; 4-chlorosuccinamide (Saraswathi et al., 2011a, 2011b, Purandara et al., 2012 and bis-3-chlorophenylmalonamide (Rodrigues et al., 2011) have been investigated as part of our studies on the substituent effect on the structures and other aspects of the bis-amides. The title compound is similar to these compounds with the difference being the length of the aliphatic chain, substituent type and position in the phenyl ring of the molecule.

Synthesis and crystallization
A mixture of glutaric acid (0.2 mol) and thionyl chloride (1.0 mol) was heated for half an hour at 363 K. Then 2nitroaniline (0.4 mol) was added dropwise under stirring. The resultant mixture was stirred for 3 h and left standing for 12 h for the completion of the reaction. The product was added to crushed ice. The white precipitate obtained was washed thoroughly with water and then with saturated sodium bicarbonate solution and again with water. It was washed first with 2 N HCl, then with water, collected by filtration, dried and recrystallized from dimethyl formamide (melting point: 503-504 K). The purity of the compound was checked by TLC and it was characterized by IR spectroscopy. The characteristic absorptions were observed at 3334.9, 1693.5 and 1330.9 cm À1  40, 35.19, 124.38, 124.65, 124.68, 131.71, 133.75, 141.36 and 170.82. Rod-shaped yellow single crystals of the title compound were obtained by slow evaporation of a DMF solution at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-bound H atoms were positioned with idealized geometry [C-H = 0.93 Å or 0.97 Å (methylene)] and refined using a riding model with U iso (H) = 1.2U eq (C). The H atoms of the NH groups were located in a difference map and later restrained to a distance of N-H = 0.86 (2) Å . They were refined with U iso (H) = 1.2 U eq (N).    (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/6 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2003); software used to prepare material for publication: SHELXL2014/6 (Sheldrick, 2015).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.3147 (